Wireless phones, laptops, PDAs, base stations, and other systems may wirelessly transmit and receive data. A single-in-single-out (SISO) system may have two transceivers in which one predominantly transmits and the other predominantly receives. The transceivers may use multiple data rates and may select from these rates based on channel quality.
A multi-antenna system, such as an MR×MT multiple-in-multiple-out (MIMO) wireless system 100, such as that shown in FIG. 1, uses MT transmit antennas 104 at a first transceiver 102 and MR receive antennas 108 at a second transceiver 106. The first and second transceivers 102 and 106 in FIG. 1 are designated “transmitter” and “receiver”, respectively, for the purposes of illustration, but both transceivers 102 and 106 may transmit and receive data.
The multiple antennas may enable the MIMO system to improve link quality (e.g., achieve a minimum bit error rate (BER)) and/or achieve high data rates. The MIMO system may improve link quality by using a transmission signaling scheme called “transmit diversity,” where the same data stream is sent on multiple transmit antennas 104, creating redundancies that may be used by the receiver 106 to obtain an estimate of the received data. The MIMO system may achieve high data rates by using a transmission signaling scheme called “spatial multiplexing,” where a data bit stream may be demultiplexed into parallel independent data streams. The independent data streams are sent on different transmit antennas 104 to obtain an increase in data rate corresponding to the number of transmit antennas 104 used. The MIMO system may use a combination of these two techniques to achieve at least some of the benefits of both techniques.
SISO and MIMO systems may use channel estimation techniques to determine the quality of the channel(s) over which data is being exchanged in the wireless system. The transmitter may transmit training sequences, which include symbols known to the receiver, for channel estimation. For a MIMO system, channels between all pairs of the transmit (Tx) and receive antennas (Rx) should be estimated. This may require extra training overhead.